Step 7: Populate your PCB with parts

Step 8: Mistakes

-Having the LEDs too close to the printed circuit board in the light box. The LEDs need to be sufficiently far enough for light to spread evenly thro...

This instructable shows how to create well done PCB's using Ultraviolet light. It took us about 40 boards before we perfected our PCB, so we will share what worked and what didn't work. All the supplies can be bought from Fry's Electronics, Ace Hardware, Goodwill, Radio Shack, and Ebay . Our PCB tested the Atmel 208 pin PQFP Integrated Circuit (it may not look like it from the poor image quality but there were no shorts between all 208 pins! ).

Thanks for the writeup! Question about the developer solution. About how many uses did you get from 2-3/4 C mixture you made? Is it like etching solution where it loses potency after several uses?

FYI - I know your UV board is already built, but for those that have not it would probably be better to run 3 LEDs in series with a 30-90 ohm resistor (depending on actual LED voltage). It would save a lot of power loss and heat dissipation, not to mention less soldering :)

Hi.I have bought this UV leds from the same seller on ebay and they are ok. I think that maybe seller has sent you wrong LED diodes. They also sell infrared LED diodes and human eye can not see that light , maybe you can see only small red dot in the middle of LED diode. You can make one test , point your camera on this LED , and you will se light which this diode is producing on your camera if that is the case then you have wrong diode.

I am not sure on the mcd rating of the LEDs. I bought the LEDs from a seller on ebay, he did not provide the mcd rating. If you search for "UV LED" in ebay, I purchased the ones for sale by Asia Engineer.

Looks good, definitely on my to do list. Glass doesn't block UV in the 400nm range so it's the best bet. Some plastic does but most should be alright sins 400nm is borderline and is actually in the visible spectrum.

My boards are not far from the leds and they' ve came out ok. Though I am using straw hat leds and I also have a diffused piece of plexi over the top of them. What are you using to cut your boards? I can't get a clean straight edge to save my life.

I also used the acetone a few times but have switched to using a solution of water and 3-5% lye drain cleaner. I just let my boards sit in the solution for a few seconds and they come out shinny and resist free.

Looks awesome! Did you have any troubles with the LEDs being too close to the PCB? You can see a picture of a failed PCB on my last page where the PCB was too close and you can see the holes of the LEDs on the photoresist.

You can solve LED distance problem by puting 2 sheets of tracing paper over LEDs. Paper sheets should be separated 5mm minimum. Two layers of tracing paper will blur UV light, without inerfering with its intensity. That's the way I did it, works good, and I use 20 degree LEDs on 4cm distance.

Thanks for the project. Just one advice; LED powering system you're using is rather inefficient, only 29% percent efficiency, you're using 41W to power up 12W worth of LED's. You might consider some circuitry to drive LED's more efficiently, or maybe chain 2 LED's in series at least, this way you could increase efficiency to about 63%. Other more efficient solutions require more complicated and expensive circuitry (like max LED drivers, or constant current circuitry).

Yup, you're right. The reason I didn't put a couple LEDs in series was because the LEDs came with 470 ohm resistors and I didn't want to buy more resistors. Something like a 5V buck DC/DC converter would be pretty cool to add in the box (something like an LTC3835), maybe I'll make a PCB for one.

If you want to produce more than one PCB, this method allows you to make more than on PCB with the same transparency. The other method (assuming the iron on method), you have to print out a new transparency every time.

You will be able to accomplish thinner traces by using the UV light method.

The main reason I chose this method was because I tried the iron on method and could not get the ink to stick to the PCB. Plus I had fun making the lightbox :)

Also, MG chemicals now has negative dry film resist. All you need is a laminater to put the film on a copper clad board. The resist is exposed with a daylight fluorescent lamp One can do single or double sided boards. The only draw back is you have to work under a yellow or red light like you would in a dark room.

Way better boards from this method. I thought using LEDs to build an exposure box would be kind of expensive so I went out and bought a fluorescent black light for $15 to do the exposure. An 8 minute exposure time worked great. Plus you can reuse your artwork.

Hi, I' using the same method to make my own PCB. I didn't have to waste 40 pcb to get good result :) I first did a test pattern ( 5mil to 50 mil lines on a small 1"x6" pcb) to find the best exposure time. You can see it in my gallery. I've attached my third PCB. It's a small i2c digital volume control for an Amp I'm currently building. The only issue I have is that my design is wrong. I grounded a pin that shouldn't be grounded. Anyway it was easy to repair with a small cut and 2 jumper wire. The second picture show a little "too much copper" under the "OUT" wire pad. The text is 3 or 4 mill I think. I'm using Staple Ink jet transparency paper (somewhat textured) and print at 600DPI. Stacking 2 or 3 layers is the key, you will get a perfectly dark (no light pass trough) pattern. Also, do not click "Print in Black only" (or gray scale) in your printer setting, the mix of color ink in the black ink seem to works better at blocking light than black ink only... I use the same mg chemical board with 3:30min exposure time.